For maximum efficiency it is desirable to operate gas turbines at an ultimate maximum temperature. This pushes the materials to their limits with many attempts being made to find ways to limit peak metal temperatures.
A local hot streak of gas may exhaust from the combustor, and with fixed vanes this can exceed the tolerable metal temperature of a vane sitting in this hot streak. Since the turbine blades are rotating they do not experience the soaking in such a high temperature location.
Gases conventionally pass through the turbine vanes or blades then through openings in the blades for the purpose of cooling. This is conventional film cooling where the exiting gas is carefully introduced to form a protective film over the surface of the blades or vanes. In obtaining such cooling gas, it must necessarily be withdrawn from areas where it could be more effectively used to produce power.
For gas turbine apparatus and flying vehicles weight is considerably important and any reduction in weight of the gas turbine can result in substantial pay off.
Previous turbine cooling studies for actively cooled rocket turbines have shown little or no payoff even assuming the most optimistic cooling effectiveness. The extensive cooling air required and the weight requirements in proportion to the weight of the turbine have not been shown to be productive.